This invention relates generally to pressure sensors and more particularly to a packaging and sealing system for fluid pressure transducers.
Pressure sensors containing pressure transducers are well known, typical such systems being described in U.S. Pat. Nos. 4,716,492, 4,774,626, 4,888,662 and 4,903,164.
Pressure transducers of the prior art have generally been fabricated by providing a pressure sensing module including an electronic circuit having a variable capacitor responsive to fluid pressure. The electronic circuit sensed the capacitance of the capacitor and provided an output through a plastic electrical connector indicative of the sensed pressure. The transducer elements were arranged such that a metal cup assembly having an opening or fluid pressure inlet at one end thereof to receive the fluid under pressure to be measured also included therein the pressure sensing module. The pressure sensing module was spaced from the inlet by a gasket or o-ring, the electronic circuit and connector also being contained within the metal cup. The parts were held together within the metal cup by crimping the metal cup over the plastic connector.
The above described pressure transducer provides highly satisfactory results when operated with certain fluids and within certain pressure ranges however a need has developed to provide a transducer which can be used in various environments and fluids including some which are corrosive in nature or hazardous in some respect with a concomitant need to prevent leakage of either the fluid being sensed to the transducer chamber housing the electronic circuitry or even the environment in general. In certain other applications it is necessary to prevent the atmosphere of the environment from leaking into the transducer chamber which could otherwise result in some deleterious effect on the electronics, such as corrosion.
Attempts have been made to provide a hermetic seal between the pressure sensing module and the metallic housing around the fluid inlet of the housing, for example by providing a transition element composed of ceramic and metal, ceramic for connection to the pressure sensing module and metal for connection to the housing, however due in part to the small size of the component parts it is very difficult to avoid damaging the ceramic to metal seal from the heat caused by the welding procedure needed to join the metal parts together.